The present to a process for the conversion of N-oxides to aldehydes, and more particularly, to the conversion tertiary amine N-oxides to aldehydes. It further relates to the field of aldehyde synthesis.
In the prior art, the Polonowsky reaction has been used to convert tertiary amine N-oxides containing at least one methyl group to secondary amines and formaldehyde in the presence of an excess of acetic anhydride.
Takabe et al., Synthetic Communications, 13(4) 297-301, (1983) recognize the use of this reaction in terpene synthesis. U.S. Pat. No. 4,447,649 also recognizes the use of this reaction for the preparation of citral from N-dialkylgeranylamine N-oxide.
These prior art reactions, however, have the drawback that they consume excess acetic anhydride and do not permit recycling of the secondary amine. This twofold drawback constitutes a considerable impediment to exploitation of the process on an industrial level.
In an effort to remedy these drawbacks, various other converting agents, instead of acetic anhydride, have been proposed. Henbest et al., Amine Oxydation part I, 3035, (1957) uses MnO.sub.2 Lecher et al., J. Am. Chem. Soc. 70, 3789, (1948) uses SO.sub.2. Various metal salts have also been proposed.
Of particular interest is the work of Fish et al. in the J. Am. Chem. Soc., 78, 3668, (1956) on the rearrangements of N-oxides in the presence of ferric ions.
Finally, Ferris et al. in the J. Org. Chem. 33, 3493, (1968) and Craig et al. in the J. Am. Chem. Soc. 83, 1871, (1961) showed that it was possible to use metals other than iron, particularly transition metals such as ruthenium, osmium and vanadium. However, with respect to vanadium, only its activity with respect to the conversion of trimethylamine N-oxide was shown. Moreover, this reaction was performed only in a very dilute aqueous medium in the presence of very large quantities of transition metal. For example, vanadium oxydichloride (VOCl.sub.2) was used in an amount of three times the amount of N-oxide. This cannot be regarded as catalysis and it leads to the formation of formic acid. Under these conditions the vast consumption of metal derivative, the very high acidity of the reaction medium (pH 1.5) and the high degree of dilution make it nearly impossible to use this process on an industrial basis. In addition, the process only provides average yields.